1. Field of the Invention
The present invention relates to a method of processing a color image and, more particularly, to a color image processing method in the case where the color reproducing range of the output system differs from the color reproducing range of the input system.
The invention also relates to a color image processing method whereby a color image signal of the input system having wide reproducing ranges of, for example, the brightness and saturation of a television image signal or the like is converted into a color image signal of the output system having the narrow reproducing ranges such as a color printer or the like.
2. Related Background Art
An ink jet video printer for reproducing a color television signal by an ink jet printer will now be described hereinbelow as an example.
Generally, in such an apparatus, the color reproducing range of the input system differs from the color reproducing range of the output system. For example, as shown in an x-y chromaticity diagram (CIE chromaticity diagram) of FIG. 1, a color reproducing range R.sub.TV in a color television is wider than a color reproducing range R.sub.IJ in a color ink jet printer. R.sub.FULL denotes a full color range in the natural world.
Hitherto, in particular, there was no method of solving such a problem. Therefore, if it is intended to reproduce the colors which cannot be reproduced by the ink jet printer as shown at, for example, A and B in FIG. 1, they are equivalently reproduced as A' and B'. Thus, the inherent saturation difference and gradation difference between A and B are lost.
Such a phenomenon is particularly typical in the case of the colors of the high purity such as, red rose, deep blue sea, and the like and causes the reproduced image quality to deteriorate remarkably.
This point will now be further described with reference to another chromaticity diagram. Referring now to FIG. 2, the ordinate axis indicates a brightness L* and the abscissa axis denotes a saturation C*=.sqroot.u*.sup.2 +c*.sup.2. It will be understood from FIG. 2 that when comparing the color reproducing range R.sub.TV of the red hue (tan.sup.-1(v/u) =70.degree.) in the television with the color reproducing ranges R.sub.IJ of the ink jet printer, the former is fairly wider than the latter. Therefore, in the case of reproducing the television image by the ink jet printer, the image of the portion in the range R.sub.TV excluding the range R.sub.IJ is condensed onto the borderline and becomes the extremely unnatural image. This problem cannot be avoided, particularly, in a full color printer because the ideal coloring agents of color inks and color toners and the like do not exist at present.
In spite of the fact that such problems are the fundamental and significant problems in this kind of apparatus as mentioned above, they have conventionally hardly been considered.